The present invention relates to a scroll-type refrigerator compressor.
In a known way, a scroll type refrigerator compressor comprises first and second volutes describing an orbital relative movement, each volute including a plate from which a spiral extends, the two spirals being engaged one inside the other and delimiting pairs of compression chambers of variable volume, the compression chambers having a volume which gradually decreases from the outside, where admission of refrigerant gas is accomplished inwards.
Thus, during the orbital relative movement of the first and second volutes, the refrigerant gas is compressed because of the reduction in the volume of the compression chambers and conveyed to the centre of the first and second volutes. The compressed refrigerant gas in the central portion flows out towards a recovery chamber via a discharge orifice made in one of the first and second volutes.
In order to improve the performances of such a compressor according to the seasons, and more particularly according to the demand for cold it is known how to make compressors with variable capacity and with variable compression level.
Document U.S. Pat. No. 7,100,386 describes a scroll-type refrigerator compressor with variable capacity comprising an orifice for letting through a refrigerant gas, made in the plate of one of the volutes and opening into one of the compression chambers.
This compressor further comprises a bypass circuit communicating with the passage orifice and a bypass valve arranged for diverting a portion of the refrigerant gas contained in the compression chambers towards the low pressure side of the compressor. With these arrangements it is possible to reduce the capacity or cylinder volume of the compressor.
This compressor also comprises a circuit for injecting refrigerant gas, communicating with the passage orifice and an injection valve arranged for injecting refrigerant gas into the compression chambers towards the low pressure side of the compressor. With these arrangements it is possible to increase the capacity of the compressor.
Thus, by suitably controlling the opening and closing of the injection and bypass valves, it is possible to adapt the capacity of the compressor according to the demand for cold.
According to a first embodiment described in document U.S. Pat. No. 7,100,386, the injection and bypass valves are both arranged outside the compressor. According to a second embodiment described in U.S. Pat. No. 7,100,386, the injection valve is arranged outside the compressor and the bypass valve is arranged in the suction stage.
Consequently, the distances between the passage orifice and the injection and bypass valves are significant, which generates a significant dead space.
Thus, when one of the valves or when both valves are in the closed position, a significant amount of refrigerant gas may flow through the passage orifice of the compression chambers towards the dead spaces of the injection and/or bypass circuits.
Now, since the pressure in each compression chamber varies from a minimum value to a maximum value during the orbital relative movement of the first and second volutes, the result of this is the occurrence of pressure pulsations in the injection and/or bypass circuits. These pressure pulsations cause overpressures and depressions in the compression chambers which may be detrimental to the performances of the compressor.
In order to overcome these drawbacks, positioning an anti-return device in proximity to the orifice for letting through refrigerant gas, made in the plate of the fixed volute, is known from document U.S. Pat. No. 4,475,360.
For this purpose, the surface of the plate of the fixed volute turned towards the side opposite to the spirals comprises a housing in which an anti-return device is mounted. The anti-return device is mobile between an open position allowing refrigerant gas to be injected into the compression chamber into which the passage orifice opens out, and a closed position preventing backflow of refrigerant gas from said compression chamber towards the refrigerant gas injection means.
With these arrangements it is possible to avoid the generation of significant dead space and therefore the occurrence of pressure fluctuations which may reduce the performances of the compressor.
However, installing an anti-return device on the upper surface of the fixed volute of a compressor may prove to be difficult, or even impossible notably when the access to the upper portion of the fixed volute is hindered by the existence of a bell covering the fixed volute or by the presence of seal elements at the discharge orifice.